In the field of communications, it is known to make multipoint transmissions, i.e. transmissions from one source to a plurality of receivers. Examples of such multipoint transmissions are multicast and broadcast transmissions. Thus the term “multipoint transmission” is used generically in the present application and claims to describe point-to-multipoint communications.
Mechanisms for multicast (e.g. sending data to a defined group of receivers, each being addressable in a multicast scheme) and broadcast (sending data to an unknown number of receivers, e.g. by using a broadcast channel to which receivers can listen) communication are sometimes provided together in a common conceptional framework, e.g. in the Multimedia Broadcast Multicast Service (MBMS) as defined by 3GPP.
An example of a network structure for multipoint transmissions is shown in FIG. 1. A content source 100 (e.g. a server in the Internet) supplies content to a multipoint transmission service center 101 in a given communication network 107, e.g. a core network of mobile communication network. The multipoint transmission service center 101 can then appropriately format the content into multipoint transmissions and perform appropriate signalling downstream via further entities 102, 103 and 104, towards multipoint receivers 1050 and 1060, shown as mobile terminals in the schematic example of FIG. 1. Taking MBMS as an example, entity 101 could be a Broadcast Multicast Service Center (BM-SC), 102 could be a Gateway GPRS Service Node (GGSN), entity 103 could be a Serving GPRS Service Node (SGSN), and entity 104 can be an access network or element of such an access network, such as a UMTS Terrestrial Radio Access Network (UTRAN).